1 files changed, 26 insertions, 7 deletions

diff --git a/storage/filesystem/dotgit/dotgit.go b/storage/filesystem/dotgit/dotgit.go
index 31c4694..72c9ccf 100644
--- a/storage/filesystem/dotgit/dotgit.go
+++ b/storage/filesystem/dotgit/dotgit.go
@@ -72,6 +72,9 @@ var (
 	// ErrIsDir is returned when a reference file is attempting to be read,
 	// but the path specified is a directory.
 	ErrIsDir = errors.New("reference path is a directory")
+	// ErrEmptyRefFile is returned when a reference file is attempted to be read,
+	// but the file is empty
+	ErrEmptyRefFile = errors.New("ref file is empty")
 )
 
 // Options holds configuration for the storage.
@@ -249,7 +252,7 @@ func (d *DotGit) objectPacks() ([]plumbing.Hash, error) {
 			continue
 		}
 
-		h := plumbing.NewHash(n[5 : len(n)-5]) //pack-(hash).pack
+		h := plumbing.NewHash(n[5 : len(n)-5]) // pack-(hash).pack
 		if h.IsZero() {
 			// Ignore files with badly-formatted names.
 			continue
@@ -661,18 +664,33 @@ func (d *DotGit) readReferenceFrom(rd io.Reader, name string) (ref *plumbing.Ref
 		return nil, err
 	}
 
+	if len(b) == 0 {
+		return nil, ErrEmptyRefFile
+	}
+
 	line := strings.TrimSpace(string(b))
 	return plumbing.NewReferenceFromStrings(name, line), nil
 }
 
+// checkReferenceAndTruncate reads the reference from the given file, or the `pack-refs` file if
+// the file was empty. Then it checks that the old reference matches the stored reference and
+// truncates the file.
 func (d *DotGit) checkReferenceAndTruncate(f billy.File, old *plumbing.Reference) error {
 	if old == nil {
 		return nil
 	}
+
 	ref, err := d.readReferenceFrom(f, old.Name().String())
+	if errors.Is(err, ErrEmptyRefFile) {
+		// This may happen if the reference is being read from a newly created file.
+		// In that case, try getting the reference from the packed refs file.
+		ref, err = d.packedRef(old.Name())
+	}
+
 	if err != nil {
 		return err
 	}
+
 	if ref.Hash() != old.Hash() {
 		return storage.ErrReferenceHasChanged
 	}
@@ -701,16 +719,16 @@ func (d *DotGit) SetRef(r, old *plumbing.Reference) error {
 // Symbolic references are resolved and included in the output.
 func (d *DotGit) Refs() ([]*plumbing.Reference, error) {
 	var refs []*plumbing.Reference
-	var seen = make(map[plumbing.ReferenceName]bool)
-	if err := d.addRefsFromRefDir(&refs, seen); err != nil {
+	seen := make(map[plumbing.ReferenceName]bool)
+	if err := d.addRefFromHEAD(&refs); err != nil {
 		return nil, err
 	}
 
-	if err := d.addRefsFromPackedRefs(&refs, seen); err != nil {
+	if err := d.addRefsFromRefDir(&refs, seen); err != nil {
 		return nil, err
 	}
 
-	if err := d.addRefFromHEAD(&refs); err != nil {
+	if err := d.addRefsFromPackedRefs(&refs, seen); err != nil {
 		return nil, err
 	}
 
@@ -815,7 +833,8 @@ func (d *DotGit) addRefsFromPackedRefsFile(refs *[]*plumbing.Reference, f billy.
 }
 
 func (d *DotGit) openAndLockPackedRefs(doCreate bool) (
-	pr billy.File, err error) {
+	pr billy.File, err error,
+) {
 	var f billy.File
 	defer func() {
 		if err != nil && f != nil {
@@ -1020,7 +1039,7 @@ func (d *DotGit) readReferenceFile(path, name string) (ref *plumbing.Reference,
 
 func (d *DotGit) CountLooseRefs() (int, error) {
 	var refs []*plumbing.Reference
-	var seen = make(map[plumbing.ReferenceName]bool)
+	seen := make(map[plumbing.ReferenceName]bool)
 	if err := d.addRefsFromRefDir(&refs, seen); err != nil {
 		return 0, err
 	}